1. Field of the Invention
The present invention relates to an improved tissue processor apparatus and related method; more particularly the present invention relates to an improved which minimizes the deterioration of the tissue during the transition between processing steps.
2. Description of the Related Art
Tissue processors are used to condition samples of tissue for microscopic examination. The tissue samples are typically fragile biological samples which can easily be damaged. The samples are prepared by being sequentially exposed to fixing, treating or staining liquids. As part of the preparation, the samples are embedded in a vehicle that gives the specimen structural integrity. A useful vehicle is a paraffin wax which is applied in a molten form.
The tissue samples are placed in a process chamber. The chamber is sealed and filled and drained with various processing reagents. The samples are finally submerged in molten paraffin wax. The samples are thereby subjected to continually changing thermal conditions the feeding and removal from the process chamber of a variety of liquids which can include molten paraffin wax. The fragile tissue samples can be damaged during the immersion and removal of liquids including molten paraffin wax. Because the tissue samples are typically biological in nature they are susceptible to thermal degradation. That is, if the tissue samples are subjected to unwanted high temperatures they can "cook". This can occur when the chamber is empty and being preheated to receive the next liquid in sequence which can include molten paraffin wax. A continuing goal is to prepare tissue samples using a process which minimizes or prevents sample deterioration.
U.S. Re. Ser. No. 29,073 and U.S. Pat. No. 4,000,460 describe a tissue processing apparatus and method. These references disclose the use of a plurality of containers of treating liquids, including paraffin. The tissue specimens are confined in the processing chamber under sealed cover and remain stationary during processing. The various liquids are directed to the processing chamber in a programmed seqence. Liquids are drawn to a sealed processing chamber by vacuum in the chamber and returned to the containers by pressure applied to the chamber. Containers of liquid paraffin wax are arranged in immediate proximity to the processing chamber. This keeps the processing chamber at a higher temperature so that the paraffin is received and remains in molten form in the chamber.
According to the disclosed method vacuum is applied to the process chamber to draw reagent liquid into the chamber from a reagent container. When the reagent container is empty, air is drawn into the process chamber, increasing the chamber pressure. The increase in chamber pressure is detected and indicates to the system that all of the liquid has been transferred. However, the air drawn through the bottom of the process chamber agitates and can damage the tissue.
Another problem with existing tissue processors is the time to transfer reagents and paraffin from their respective containers to the process chamber and back. It can take on the order of five minutes to fill and drain the process chamber. As a result, those tissue samples located in the upper portion of the process chamber can be left exposed, i.e. not in contact with liquid for up to ten minutes per processing step of which there can be up to fifteen. This can result in significant discrepancies in the quality of the processed tissue samples within the same batch depending upon their location in the process chamber.
In the disclosed processes molten paraffin is drawn to the process chamber. However the chamber must be preheated and void of other liquid. If these conditions are not met, paraffin entering the bottom of the process chamber will solidify and prevent further filling of the chamber. Further, the preheating of the process chamber in the absence of liquids causes samples to be exposed to excessive heat which can cook the tissue.
There is disclosed a method for controlling liquid level in the process chamber by applying a vacuum for a predetermined time period. This method is inaccurate due to differences in liquid paths in the system. This can result in exposed tissue when not enough liquid is brought to the process chamber.
The disclosed processes have the disadvantages of sample deterioration by both liquid movement and by heat transfer. These are attributable to the sequential addition and removal of liquids which physically contact the samples. Additionally, the introduction of molten paraffin into the process chamber typically requires preheating the chamber to prevent paraffin solidification. This preheating can "cook" the sample.